Process for increasing the catalytic activity of titanium trichloride



United States Patent 3,134,642 PROCESS FOR INCREASING THE CATALYTICACTIVITY OF THTANTUM TRICHLORIDE Thomas S. Mertes, Wilmington, Del.,assignor-to Sun Oil Company, Philadelphia, Pa., a corporation of Newersey N0 Drawing. Original application Nov. 27, 1957, Ser. No. 699,196,now Patent No. 2,968,652, dated Jan. 17, 1961. Divided and thisapplication May 16, 1960, Ser. No. 29,180

1 Claim. (Cl. 23--87) This invention relates to a new process for thepreparation of relatively high molecular weight polymers, and moreparticularly relates to a process for the preparation of solid polymersof alpha-olefins, whereby much smaller quantities of catalyst are usedthan have heretofore been possible.

Alpha-olefins such as propylene have heretofore been polymerized to highmolecular Weight solid polymers. A

catalyst which is especially effective for the polymerization ofalpha-olefins to such relatively high molecular weight sol-id polymersis a lower halide of titanium, such as titanium trichloride, activatedby an aluminumtrialkyl, such as aluminum triethyl. The titaniumtrichloride is dis persed in a finely divided solid form in an inertsolvent such as isooctane, and the aluminum trialkyl admixed therewith.In performing the polymerization step, an alpha-olefin is contacted withthe catalyst and activator, such as by passing the olefin through asuspension of the catalyst in the inert reaction medium, and isthereby'polymerized to solid polymers. Other materials can besubstituted for the titanium trichloride and/or aluminum triethyl, ashereinafter described. Anhydrous and oxygenfree conditions are usedthroughout the process, since the catalyst is deactivated by contactwith water or oxygen.

Polymerization proceeds quite rapidly in this system, solid polymerforming on the solid catalyst particles. The polymer formed on thecatalyst particles eventually completely coats the particles, so thatthey no longer promote polymerization, and polymerization ceases. Acatalyst deactivating material, such as water or an alcohol is added tothe reaction mixture and the mixture is agitated, preferably by meanswhich comminute the polymer so that catalyst particles embedded in thepolymer are exposed to the deactivant. Thereafter, in order to removethe inorganic catalyst or the'inorganic particles resulting from thecatalyst deactivation, the reaction mixture is contacted with a stronginorganic acid such as an aqueous or alcoholic solution of nitric acid.The solid polymer is then separated from the acid solution and is washedand dried. A major proportion, usually 50% to 75%, of the polymerproduced by this process is crystalline, i.e., exhibits a crystallinestructure by X-ray analysis. This crystalline polymer usually has amolecular weight of 50,000 to 500,000 or more, a melting point of 160 C.to 170 C., and a yield strength in tension of 3800 to 5000 p.s.i. Aproduct having a high proportion of crystalline polymer is especiallydesirable, because of its superior properties. Polyolefins produced bythis method may be extruded into films for wrapping materials, or may bemolded or otherwise formed into containers and many other usefularticles.

In the process hereinbefore described, the rate of polymerization andamount of polymer formed is related to the amount of catalyst used,since the catalyst particles become coated with polymer, and aretherefore made inactive, during the polymerization. From thisstandpoint, therefore, a fairly high proportion of catalyst isdesirable. However, the catalysts used are quite expensive, and inaddition are difiicult to remove from the polymer. It is essential thatthe finished polymer be substantially free of catalyst, sincecontaminants discolor and weaken the polymer. It is evident, therefore,that it is undesirable to use large quantities of catalyst.

Titanium trichloride of commerce is a granular material having particlesas large as 250 microns or larger, and an average particle size of 15 to40 microns. Other materials used as catalysts in this process are in asimilar form. It has now been found that if these catalyst particles arereduced in size, a much higher rate and yield of polymerization isobtained with no increase in the amount of catalyst used or in otherconditions of the polymerization reaction. In addition, the more finelydivided catalyst produces a product which has a much higher proportionof crystalline polymer, and which has a more uniform molecular weight.

It is an object of this invention to provide a method wherebyalpha-olefins may be polymerized at a relatively high rate and yieldwith a smaller quantity of catalyst than has heretofore been possible.It is another object to provide a method whereby alpha-olefins may bepolymerized to predominantly crystalline polymers of relatively uniformmolecular weight. Still another object is to provide a method wherebysolid catalysts used in the polymerization of olefins may be reduced toextremely finely divided particles and are thereafter contacted with anolefin and an activator for the catalyst, whereby predominantlycrystalline polymers of the olefin are produced. A further object is toprovide a method for preparing predominantly crystalline polymers ofolefins which are substantially free of contamination by catalystparticles.

These and other objects of this invention are attained by subjecting adispersion of catalyst particles in an inert liquid to ultrasonic wavesof an intensity such that the catalyst particles are broken down intoextremely finely divided particles, and then adding this catalyst to areaction mixture of olefin and catalyst activator in an inert, liquidreaction medium, whereby the olefin is polymerized to high molecularweight solid polymers. Alternatively,

the catalyst may first be contacted with the catalyst activator and thensubjected to the ulrasonic waves.

Although the process of this invention is applicable to alpha-olefinsgenerally, that is, to olefins having a terminal double bond, forconvenience the present process is described largely in terms ofpolymerizing propylene to form is used may be a parafiinic hydrocarbon,such as the hexanes, heptanes, octanes, nonanes, decanes and mixturesthereof and the like, or a cycloparaffinic hydrocarbon such ascyclohexane, methyl cyclopentane, decahydronaphthalene and mixturesthereof with each other'and with paraffins, or with aromatics such asbenzene, toluene and the like.

The solid catalyst materials used are in a particulate form. Usually thematerial has been ground or otherwise comminuted to a particle size ofnot more than 500 microns. Upon subjecting the inert liquid containingthese particles to ultrasonic waves, particles are broken down to suchsmall size that they remain suspended for much longer periods of time,or with greatly reduced agitation can be kept continuously insuspension.

By ultrasonic waves, as used herein, is meant the vibratory waves of afrequency above the limit of the although intensities as low as one wattgive good results, and much higher intensities, up to about 1000 wattsper square centimeter, may be used. The conversion of energy intoultrasonic waves by the use of transducers is well-known. By the termtransducer, as used herein, is meant means for converting energy intoultrasonic waves within the limits herein described. Means which utilizethe piezoelectric effect, e.g., as exhibited by quartz and bariumtitanate, give good result and are preferred, but other means, such asthe magnetostrictive devices, may be used if desired. It is believedthat the ultrasonic waves employed in the processes of the inventionproduce cavitation throughout the inert liquid, and especially adjacentthe catalyst particles, and. that this cavitation produces extremelyhigh stresses in the catalyst particles, causing them to bedisintegrated into very finely divided particles, usually from about 0.1to about 5.0 microns in size, and averaging less than 1.0 micron. Theextreme agitation produced by the ultrasonic waves causes theseparticles to be uniformly dispersed through the inert liquid, and due tothe fineness of the particles, they remain suspended after thepropagation of ultrasonic Waves has ceased.

Although the preferred catalyst for practiciing this invention is alower halide of titanium, other halides of the metals of groups IV, Vand VI of the periodic table may also be employed. Preferably a halideof titanium, zirconium, hafnium, vanadium, niobium, chromium, molybdenumor tungsten is used. The metal of the metal compound must be in avalence other than its highest valence state, and the metal compoundmust be a solid. Among the catalysts which may be used are includedtitanium trichloride, titanium dichloride, titanium tribromide, titaniumtriiodide, zirconium trifluoride, vanadium trichloride and chromiumtrichloride. These materials may be prepared by reacting a highervalence metal halide with a suitable reducing agent, such as the metalalkyls, metal hydrides, metal borohydrides, and metal alkyl halideswhich are described hereinafter as being suitable activators for thecatalysts of this invention. Thus a metal halide such as titaniumtetrachloride, tetrafiuoride, tetrabromide or tetraiodide, and thecorresponding higher valence halides of the other metals of groups IV, Vand VT may be reacted with an activator so that the lower valence formof the metal halide is formed, and the reaction product subjected to theultrasonic waves. This reaction product is in solid form and includes alower valence form of the metal halide used. Whether the higher valencemetal halide or the lower valence metal halide is used, it may be mixedwith the activator therefor either before or after it is subjected tothe ultrasonic waves.

The disintegrated catalyst, in an inert liquid, is added to thepolymerization reaction mixture, which consists of an inert liquidreaction medium, an alpha-olefin, and an activator for the catalyst. Thereaction medium may be a saturated hydrocarbon such as the hexanes,heptanes, octanes, decanes, cyclopentanes, cyclohexanes, mixturesthereof and the like which are liquid under the conditions of reaction.The reaction medium may also include aromatic hydrocarbons up to about25% without deleterious effects. Usually, the olefin is added to thereaction medium before the catalyst and activator are added, althoughthe constituents may be added in any order. Polymerization is performedunder polymerizing conditions, including a temperature of from about C.to 250 C., and a pressure of from atmospheric to 10,000 p.s.i.g. (poundsper square inch gauge) or more, it being necessary that the reactionmedium be maintained in the liquid phase.

The activator used is preferably an aluminum trialkyl, such as aluminumtriethyl, however, other materials which are also suitable activatorsinclude other metal alkyls, metal hydrides, metal borohydrides and alkylmetal halides. Suitable metal alkyls include alkyl derivatives ofaluminum, zinc, beryllium, chromium, magnesium, lithium and lead.Aluminum triethyl, aluminum triisopropyl, aluminum triisobutyl and themagnesium and zinc analogues thereof give good results in the processand are preferred, but metal alkyls having up to about 12 carbon atomsin the alkyl groups can be used with good results. Alkali metal alkylssuch as n-butyl lithium, methyl sodium, butyl sodium, phenyl isopropylpotassium, and the like, also illustrate metal alkyls that give goodresults in the process. Metal hydrides which can be used aspolymerization activators include, for example, lithium hydride, lithiumaluminum hydride and sodium hydride. Metal borohydrides such as sodiumborohydride and potassium borohydride illustrate the borohydrides whichcan be used. Alkyl metal halides which can be used include Grignardreagents such as methyl magnesium bromide, ethyl magnesium chloride,phenyl magnesium bromide and other alkyl metal halides such as diethylaluminum chloride and ethyl aluminum dichloride.

The quantities of catalytic components can be varied and good resultsobtained. A mole ratio of catalyst to activator of from 1:12 to 10:1gives good results. The amount of reaction medium used may vary fromabout 500 to about 50,000 times the weight of catalyst used. Since thecatalyst is in an extremely finely divided form, a relatively smallamount of catalyst may easily be dispersed throughout a larger amount ofreaction medium, thereby providing a large number of nuclei about whichpolymerization can take place. When catalyst which has not beenirradiated with ultarsonie waves is used, at least several times as muchcatalyst, say about 10 times as much catalyst, may be required to obtainequivalent results, due in part to the fact that fewer particles perunit Weight are available to form nuclei for polymerization.

Although the steps hereinbefore described are essentially those of abatch process, the process of this invention is equally adaptable tocontinuous operation. For example, the catalyst particles may beinjected continuously into a stream of inert liquid, and the liquid becontinuously flowed through an ultrasonics zone, at a evlocity such thatthe catalyst particles remain in the ultrasonics zone long enough to bedisintegrated. The catalyst and inert liquid may then be injected into areactor where the olefin and activator are being continuously injectedand where solid polymer is being continuously removed.

After the polymerization step, the solid polymer is separated from thereaction medium, and a catalyst deactivating material, such as water oralcohol, is added to the polymer. The polymer is then ground, chopped orotherwise comminuted in the presence of the deactivator, so that thecatalyst particles are exposed and deactivated. The liquid deactivant isthen removed from the polymer such as by draining or filtering, and thepolymer washed with a dilute inorganic acid, such as nitric acid, towash out the catalyst and other inorganic material.

The polymer obtained by this process is a white predominantlycrystalline solid material which is substantially free of catalystparticles and catalyst residue, usually containing less than 50 ppm.(parts per million), whereas polymer made by other processes normallyhave from 200 to 500 ppm. of such catalyst materials (calculated as themetal). Consequently, the polymer products of the present process arewhite and free of discoloration, whereas formerly only greyish oryellowish products were obtained. The polymers produced by the presentprocess therefore have much greater utility in applications whereappearance is important.

The following examples, wherein parts refers to parts by weight,illustrate the process of this invention:

Example I Titanium trichloride of commerce was examined and found tohave a minimum particle size of 2 microns, a

maximum size of 254 microns, and average size of 25 microns. One part ofthis titanium trichloride is dispersed in parts of isooctane, underanhydrous and oxygenfree conditions. A nitrogen atmosphere at 5 p.s.i.g.pressure is provided to keep out air. A piezoelectric transducer isattached to the vessel containing the isooctane, and is operated for twominutes at 50,000 cycles per second frequency, and at an intensity of 10watts per square centimeter. The titanium trichloride is broken down socompletely that the particles remain in suspension long after theultrasonic, radiation ceases. A portion of the isooctane containingsuspended titanium trichloride is heated to evaporate the isooctane. Thetitanium trichloride particles remaining are from 0.2 to 2.7 microns insize, and 70% are less than 1.0 micron.

The remaining isooctane, containing 0.95 part of suspended titaniumtrichloride, is added to a reactor containing 5,000 parts of reactionmixture, consisting of 23 weight percent of propylene and 0.6 parts ofaluminum triethyl, maintained at 85 C. to 90 C. and a pressure of 100p.s.i.g. Polymerization begins immediately, as evidenced by a decreasein the pressure in the reactor. Additional propylene is injectedperiodically tomaintain the pressure in the reactor at approximately 100p.s.i.g. After 3.1 hours, the rate of polymerization has decreasedsubstantially. Excess propylene is vented, the reaction medium drainedOE, and the remaining polymer ground in the presence of methanol. Themethanol is then drained off, and the polymer washed with dilute nitricacid, and then dried. A total of 760 parts of polypropylene are formedwhich is 96% crystalline polymer and which has an average molecularweight of 212,000. The material contains only 30 p.p.m. of titanium, andproducts molded from it are white and clear.

Example II One part of the purchased titanium trichloride is dispersedin 10 parts of isooctane and added in this form to a reactor containingthe same mixture as is described in Example I. The polymerizationreaction began in about five minutes, and proceeded for 15.3 hours.After deactivating, washing and drying, as described in Example I, 529parts of polypropylene which has an average molecular weight of 155,000is obtained. This material is crystalline polymer and contains 230p.p.m. of titanium. Products molded from it are discolored.

Example 111 The following data shows that other comminuting methods donot produce a catalyst which is equivalent in the polymerization ofolefins.

One part of the purchased titanium trichloride was ground in a ball millfor one hour in mineral oil. The resulting titanium trichloride had amaximum particle size of microns, a minimum size of 1 micron, and anaverage size of 13 microns. This material was use in the polymerizationprocess as described in Example I, using substantially the sameproportions and conditions. The polypropylene obtained was 71%crystalline, having an average molecular weight of 166,000 and contained210 ppm. of titanium. Products molded from this polymer were discolored.

Polymers produced by the process of this invention are thermoplasticsolids which may be molded, extruded, or otherwise fabricated intopiping, various containers, films for wrapping food products, and manyother useful products.

This application is a division of US. Serial No. 699,196, filed November27, 1957, now US. Patent No. 2,968,652, by the same inventor.

The invention claimed is:

A process for increasing the catalytic activity of titanium trichloridewhich comprises subjecting crystalline titanium trichloride having anaverage particle size of from 15 to 40 microns, suspended in an inertliquid, to the action of ultrasonic waves having a frequency of from20,000 to 500,000 cycles per second and an intensity of from 4 to 20watts per square centimeter for a period of time sufficient to reducethe particle size of the titanium to from 0.1 to 5.0 microns.

References Cited in the file of this patent UNITED STATES PATENTS2,893,984 Seelbach et al July 7, 1959 2,899,414 Mertes Aug. 11, 19592,925,392 Seelbach et al Feb. 16, 1960 2,968,652 Mertes Jan. 17, 1961

